Add new feature for predated posts.

Now, you have the ability to publish predated posts automatically.

![screen shot 2013-12-17 at 20 05 35](https://f.cloud.github.com/assets/722890/1767380/f8a05040-6752-11e3-8925-43d421719820.png)
![screen shot 2013-12-17 at 20 05 49](https://f.cloud.github.com/assets/722890/1767381/f8a373ec-6752-11e3-8d00-07fc9b380941.png)